Conventional metal plate cutting technologies are well known in the art. Oxy acetylene plate cutting was the universal method used in the first half of the 20th century. Electronic optically guided sheet and plate steel cutting machines appeared in the 1960s, machines which copied a drawn template by using a ‘magic eye.’
Computer guided machines appeared in the 1970s, machines which followed coordinates given in a plain English language known as Numeric Control programs or NC programs. Plasma cutting itself appeared in the 1940s as an extension of electric arc welding, carrying the very high currents in a plasma gas which melted, rather than burned, the metal.
Plasma cutting was a much faster method but gave a poor cut quality, although adequate if the edge was going to be ground for welding. For materials up to 20 mm thick a plasma torch cuts up to 10 times faster than an oxy acetylene torch. An inert plasma gas could even be used for cutting highly combustible materials such as aluminum. Another advantage of plasma cutting is that the high speed combined with the ejection of hot molten material rather than combustion of the material reduced heat input into the plate and this in turn reduced potentially large thermally induced part movement during cutting.
In the 1970s, the high speed of plasma cutting had to be balanced with the relatively poor cut with high degrees of cut edge chamfer, as high as 45 degrees. Plasma torches could also generate unbearable noise levels and large amounts of ozone. In the 1990s High Definition Plasma cutting technology was a dramatic improvement with torches and gas and power supplies developed to cut with much less chamfer, higher edge quality and narrower cut width or kerf. Modern torches claim a cut edge chamfer as low as 2 degrees from vertical. As a consequence of straighter and narrower cuts, the penetration of plasma has increased from around 50 mm to 160 mm and beyond, challenging the dominance of oxy acetylene cutting of thick steel plate. Most recently the use of air alone as the plasma gas has reduced operating costs and the noise during operation has dropped to acceptable levels in a factory environment. The rapid drop in the price of computers after 2000 meant that computer controlled shape cutting has become affordable and standard in even the smallest workshops.
Such Numeric Control machines are used to cut flat plates or sheets into single parts or a collection of such parts on a plate, which is known as a nest. The parts within the nest are positioned by an NC programmer or by automatic nesting software to waste less metal.